1. Technical Field
The present invention relates to polycyclic copolymer compositions and methods for their preparation and use. More specifically this invention concerns random copolymers comprising repeating units polymerized from cycloolefinic and acrylate monomers.
2. Background
High molecular weight polycyclic addition polymers having directly linked polycyclic repeating units without any internal backbone unsaturation are desirous from the standpoint of their inherent thermoxidative stability and high glass transition temperature (Tg) profiles. Cycloolefinic monomers such as norbomene(bicyclo[2.2.1]hept-2-ene) have been addition polymerized utilizing a variety of catalytic systems. Goodall et al. (U.S. Pat. No. 5,468,819) have successfully prepared polycyclic polymers from cycloolefinic monomers such as norbornene and hydrocarbyl substituted norbornene-type monomers. The molecular weights and Tg's of these polymers are tailored to desired specifications by conducting the polymerization in the presence of a Group VIII transition metal catalyst and an olefinic chain transfer agent.
Recent objectives in polymer synthesis have focused on the polymerization of monomers containing functional groups to obtain polymers with high Tg's and molecular weights. The incorporation of functional substituents into hydrocarbon polymer backbones is useful for modifying the chemical and other physical properties of a polymer. U.S. Pat. No. 5,705,503 to Goodall and Risse discloses polycyclic addition polymers containing functional substituents. Goodall and Risse have demonstrated that cycloolefinic monomers containing pendant polar functionality could be polymerized to polymer compositions of high molecular weight and Tg.
An alternative method for the incorporation of polar functional groups into a hydrocarbon polymer backbone has been to copolymerize the hydrocarbon monomer (e.g. an olefin) with a polar functional comonomer (e.g., an acrylate). The random copolymerization of ethylene with methyl acrylate is to date only possible using free radical initiators under extreme conditions of temperature and pressure. Very recently some progress has been made in the area of coordination copolymerization of ethylene and methyl acrylate using palladium catalysts (Brookhart et al., J. Amer. Chem. Soc., 1998, 120, 888-899 and International Published Application WO 96/23010). In this case, however, the resulting copolymers are not true random copolymers since the majority, if not all, of the acrylate repeating units are incorporated at the chain ends of the highly branched polymer products.
In the case of copolymerizing a polycycloolefin with acrylic monomers the use of coordination catalysts for the copolymerization has never been described in the art. Indeed, International Application WO 96/23010 supra discloses that when a norbornene-type monomer is polymerized, no other monomer can be present. Even more recently, Abu-Surrah and Reiger (J. Mol. Catal. A: Chem. (1998), 128, 239-243) reported that certain cationic palladium (II) compounds active in the homopolymerization of norbornene are inactive to the homopolymerization and copolymerization of polar monomers like acrylates. They further reported that addition of methacrylate to norbornene polymerization systems using the disclosed catalysts resulted simply in higher molecular weight and narrower polydispersity of the norbornene homopolymers with no evidence for acrylate incorporation into the polymer backbone.
U.S. Pat. No. 3,536,681 to Morris discloses copolymers of norbomenes and acrylates that were polymerized by free radical means. The resulting polymers were elastomers with very low levels of norbornene incorporation (i.e., up to 5.5 weight percent).
U.S. Pat. No. 3,679,490 to Starmer discloses terpolymers of substituted norbornenes, acrylates and alkoxy alkyl acrylates. These polymers are again elastomeric (having sub-zero Tg's) and contain very low levels of norbornene (i.e., up to 5.5 weight percent).
More recently Behrens in German Published Patent Application 2,358,112 disclosed copolymers of acrylates with ethylidenenorbornene.
In U.S. Pat. No. 5,585,222 to Kaimoto et al. there is disclosed copolymers suitable for use in photoresist compositions. The disclosed copolymers are prepared by copolymerizing a 2-substituted norbornene with an acrylic acid ester in the presence of an anionic catalyst system. The substituent on the 2-position of the norbornene monomer is essential to the polymerization reaction. The substituent is selected from a chloro or cyano group which serves to activate the unsaturation on the norbornene ring to anionic polymerization.
In Japanese Patent Application Publication 04063810 to Kubo there is disclosed terpolymers polymerized from norbornene, maleic anhydride, and acrylic monomers.
In European Published Patent Application 0 794 458 there is described energy sensitive resist materials made by free radically polymerizing an alicyclic monomer such as norbornene and a second monomer such as maleic anhydride. Acrylic monomers can be incorporated as a third or fourth repeating unit in the polymer. The key to the successful free radical polymerization of these mixtures is that the norbornene monomer is an electron donor and the second monomer (maleic anhydride being preferred) is an electron acceptor. Such systems are known to be facile in free radical polymerization to afford alternating copolymers as reported by Cincu et al., Macromol. Reports, A33 (suppl. 2), 83-91 (1996).
In view of the limitations of the prior art, there is a need for random copolymers containing repeating units polymerized from polycycloolefin and acrylate comonomers that contain high levels of polycycloolefin incorporation and have high glass transition temperatures, without the need for special monomer activating substituents or the inclusion of special monomers in the reaction medium.